Image sensor with heating effect and related methods

ABSTRACT

An image sensor including a semiconductor layer. A light absorber layer couples with the semiconductor layer at a pixel of the image sensor and absorbs incident light to substantially prevent the incident light from entering the semiconductor layer. The light absorber layer heats a depletion region of the semiconductor layer in response to absorbing the incident light, creating electron/hole pairs. The light absorber layer may include one or more narrow bandgap materials.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of the earlier U.S. Utilitypatent application to Lenchenkov et al. entitled “Image Sensor withHeating Effect and Related Methods,” application Ser. No. 14/723,675,filed May 28, 2015, the disclosure of which is hereby incorporatedentirely herein by reference.

BACKGROUND

1. Technical Field

Aspects of this document relate generally to image sensors. Morespecific implementations involve complementary metal-oxide-semiconductor(CMOS) image sensors.

2. Background Art

Image sensors convey information related to an image by communicatingsignals in response to incident electromagnetic radiation. Image sensorsare used in a variety of devices including smart phones, digitalcameras, night vision devices, medical imagers, and many others.Semiconductor imagers utilizing charge-coupled device (CCD) and CMOSarchitectures exist in the art.

SUMMARY

Implementations of image sensors may include: a semiconductor layer,and; a light absorber layer coupled with the semiconductor layer at apixel of the image sensor, the light absorber layer configured to absorbincident light and to substantially prevent the incident light fromentering the semiconductor layer; wherein the light absorber layer isconfigured to heat a region (heated region) of the semiconductor layerin response to absorbing the incident light and to create electron/holepairs in the heated region thereby.

Implementations of image sensors may include one, all, or any of thefollowing:

The light absorber layer may include a material selected from the groupconsisting of: Co; CoSi₂; Mo; MoSi₂; Ni; NiSi; Ni₂Si; NiSi₂; Pd; PdSi;Pd₂Si; Pt; PtSi; Ta; TaSi₂; Ti; TiSi₂; W; WSi; WSi₂; Zr; ZrSi₂;polycrystalline Si; Ge doped monocrystalline Si; Ge film on Ge dopedsilicon; GeSe film on Silicon; and any combination thereof.

A microlens may be included, the light absorber layer coupled betweenthe microlens and the semiconductor layer, the microlens configured torefract the incident IR light towards the light absorber layer.

A guide may be coupled between the microlens and the light absorberlayer and may be configured to convey the refracted light to the lightabsorber layer.

The image sensor may be a backside integrated (BSI) sensor.

The light absorber layer may be positioned between two shallow trenchesin the semiconductor layer, each shallow trench extending only partiallythrough the semiconductor layer from a backside of the semiconductorlayer towards a frontside of the semiconductor layer.

The light absorber layer may be positioned between two deep trenches ofthe semiconductor layer, each deep trench extending fully through thesemiconductor layer from a backside of the semiconductor layer throughto a frontside of the semiconductor layer.

An antireflective coating (ARC) may be coupled between the incidentlight and the light absorber layer.

The image sensor may have a quantum efficiency (QE) above 50% forphotons within a wavelength range of 0.7 to 20 microns.

Implementations of image sensors may include: a photodiode included atleast partially within a semiconductor layer, and; a light absorberlayer coupled with the photodiode, the light absorber layer configuredto absorb incident light within predetermined wavelengths tosubstantially prevent the incident light from passing from the lightabsorber layer to the photodiode; wherein the light absorber layer isconfigured to heat a depletion region of the photodiode in response toabsorbing the incident light and to create electron/hole pairs in thedepletion region thereby, and; wherein the image sensor further includesat least one dielectric layer coupled with the semiconductor layer, andelectrical routing coupled at least partially within the at least onedielectric layer which electrically couples the photodiode with at leastone other element of the image sensor.

Implementations of image sensors may include one, all, or any of thefollowing:

An antireflective coating (ARC) may be coupled between the incidentlight and the light absorber layer.

The light absorber layer may be located at a backside of thesemiconductor layer and the at least one dielectric layer may include afrontside dielectric layer coupled at a frontside of the semiconductorlayer opposite the backside of the semiconductor layer.

The light absorber layer may be located at a backside of thesemiconductor layer, a focusing element may be located proximate afrontside of the semiconductor layer opposite the backside of thesemiconductor layer, and the focusing element may be configured to focusthe incident light, that has already passed through the semiconductorlayer, back through the semiconductor layer towards the backside of thesemiconductor layer.

The light absorber layer may be located at a backside of thesemiconductor layer, the at least one dielectric layer may include afrontside dielectric layer and a backside dielectric layer, the backsidedielectric layer may be located at the backside of the semiconductorlayer, a focusing element may be located proximate the backsidedielectric layer and may be configured to focus the incident lightthrough the backside dielectric layer towards the light absorber layer,the frontside dielectric layer may be located at a frontside of thesemiconductor layer opposite the backside of the semiconductor layer,and the electrical routing of the image sensor may be included at leastpartially within the frontside dielectric layer.

The light absorber layer may be located at a frontside of thesemiconductor layer, the at least one dielectric layer may include afrontside dielectric layer coupled at the frontside of the semiconductorlayer, a focusing element may be located proximate the frontsidedielectric layer and may be configured to focus the incident lightthrough the frontside dielectric layer towards the light absorber layer,and the electrical routing of the image sensor may be included at leastpartially within the frontside dielectric layer.

The light absorber layer may include a material selected from the groupconsisting of: Co; CoSi₂; Mo; MoSi₂; Ni; NiSi; Ni₂Si; NiSi₂; Pd; PdSi;Pd₂Si; Pt; PtSi; Ta; TaSi₂; Ti; TiSi₂; W; WSi; WSi₂; Zr; ZrSi₂;polycrystalline Si; Ge doped monocrystalline Si; Ge film on Ge dopedsilicon; GeSe film on Silicon; and any combination thereof.

The light absorber layer may be positioned between two trenches in thesemiconductor layer, each trench extending at least partially throughthe semiconductor layer.

The image sensor may have a quantum efficiency (QE) above 50% forphotons within a wavelength range of 0.7 to 20 microns.

Implementations of image sensors may include: a complementarymetal-oxide-semiconductor (CMOS) device having a semiconductor layer,the semiconductor layer including a plurality of photodiodes, eachphotodiode having a pixel having a depletion region, and; a plurality oflight absorber layers, each light absorber layer coupled with one of thepixels of the semiconductor layer, each light absorber layer configuredto absorb incident light and substantially prevent the incident lightfrom entering one of the photodiodes; wherein each light absorber layeris configured to heat the depletion region of one of the photodiodes inresponse to absorbing the incident light, and to create electron/holepairs in the depletion region thereby, through an increase intemperature alone.

Implementations of image sensors may include one, all, or any of thefollowing:

The image sensor may have a quantum efficiency (QE) above 50% forphotons within a wavelength range of 0.7 to 20 microns.

The foregoing and other aspects, features, and advantages will beapparent to those artisans of ordinary skill in the art from theDESCRIPTION and DRAWINGS, and from the CLAIMS.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations will hereinafter be described in conjunction with theappended drawings, where like designations denote like elements, and:

FIG. 1 is a cross section view of an implementation of an image sensor;

FIG. 2 is a cross section view of the image sensor of FIG. 1 and anotherimplementation of an image sensor;

FIG. 3 is a cross section view of the image sensors of FIG. 2 withincident and refracted infrared (IR) light waves representativelyillustrated;

FIG. 4 is a cross section view of the image sensors of FIG. 3 withtemperature profiles of the image sensors representatively illustrated;

FIG. 5 is a graph plotting spectra of an imaginary part of complexrefractive index for TaSi₂ and c-Si as a function of wavelength;

FIG. 6 is a graph plotting imaginary index of refraction spectra for aplurality of materials as a function of wavelength;

FIG. 7 is a cross section view of implementations of image sensors;

FIG. 8 is a cross section view of implementations of image sensors;

FIG. 9 is a cross section view of implementations of image sensors;

FIG. 10 is a cross section view of implementations of image sensors;

FIG. 11A is a cross section view of an image sensor without a lightabsorbing layer (between two shallow trenches on the left) next to animage sensor with a light absorbing layer (between two deep trenches onthe right), illustrating incident and refracted light;

FIG. 11B is a cross section view of an image sensor with a lightabsorbing layer (between two shallow trenches on the left) next to animage sensor with a light absorbing layer (between two deep trenches onthe right), illustrating incident and refracted light;

FIG. 12A is a cross section view of the image sensors of FIG. 11A aftera specified amount of time has lapsed;

FIG. 12B is a cross section view of the image sensors of FIG. 11B aftera specified amount of time has lapsed;

FIG. 13A is a cross section view of the image sensors of FIG. 12A aftera specified amount of time has lapsed;

FIG. 13B is a cross section view of the image sensors of FIG. 12B aftera specified amount of time has lapsed;

FIG. 14A is a cross section view of the image sensors of FIG. 13A aftera specified amount of time has lapsed;

FIG. 14B is a cross section view of the image sensors of FIG. 13B aftera specified amount of time has lapsed;

FIG. 15A is a cross section view of the image sensors of FIG. 14A aftera specified amount of time has lapsed;

FIG. 15B is a cross section view of the image sensors of FIG. 14B aftera specified amount of time has lapsed;

FIG. 16A is a cross section view of the image sensors of FIG. 15A aftera specified amount of time has lapsed;

FIG. 16B is a cross section view of the image sensors of FIG. 15B aftera specified amount of time has lapsed;

FIG. 17A is a cross section view of the image sensors of FIG. 16A aftera specified amount of time has lapsed;

FIG. 17B is a cross section view of the image sensors of FIG. 16B aftera specified amount of time has lapsed;

FIG. 18 is a top view of a dark signal (dark current) image of a printedcircuit board (PCB) generated using a traditional image sensor without alight absorber layer;

FIG. 19 is a top view of another dark signal (dark current) image of aprinted circuit board (PCB) generated using a traditional image sensorwithout a light absorber layer, and;

FIG. 20 is a top view of another dark signal (dark current) image of aprinted circuit board (PCB) generated using a traditional image sensorwithout a light absorber layer.

DESCRIPTION

This disclosure, its aspects and implementations, are not limited to thespecific components, assembly procedures or method elements disclosedherein. Many additional components, assembly procedures and/or methodelements known in the art consistent with the intended image sensors andrelated methods will become apparent for use with particularimplementations from this disclosure. Accordingly, for example, althoughparticular implementations are disclosed, such implementations andimplementing components may comprise any shape, size, style, type,model, version, measurement, concentration, material, quantity, methodelement, step, and/or the like as is known in the art for such imagesensors and related methods, and implementing components and methods,consistent with the intended operation and methods.

As used herein, the term “image sensor” may refer both to a sensorassociated with only an individual pixel as well as to a sensorassociated with a plurality (such as an array) of pixels. As usedherein, the term “backside” refers to a side (in other words a surface)of an element corresponding with (in other words, located at, or facing)a wafer backside during fabrication. As used herein, the term“frontside” refers to a side (in other words, a surface) of an elementcorresponding with (in other words, located at, or facing) a waferfrontside during fabrication.

Referring now to FIGS. 1-2, in various implementations an image sensor(sensor) 2 is formed as a backside integrated (BSI) sensor 6 or, inother words, it is formed adjacent a wafer backside during fabrication.Image sensor 2 includes a photodiode 8 associated with a single pixel10. Trenches 42 are used for isolation purposes—in this case primarilyfor heat isolation, as is discussed herein. Shallow trenches 44 are usedwith the leftmost image sensor 2 shown in FIG. 2 and deep trenches 46are shown with the rightmost image sensor 52 shown in FIG. 2.

In FIGS. 1-2 a semiconductor layer 34 is sandwiched between twodielectric layers 28. The dielectric layers may be intermetal dielectric(IMD) or interlayer dielectric layers (ILD). The semiconductor layer inthis representative example is a silicon layer and the dielectric layersare silicon dioxide (SiO₂) layers. The trenches in the examples shown inthe drawings are formed with SiO₂ as well. One of the dielectric layersis a frontside dielectric layer 32 which corresponds with (or in otherwords is located at) a wafer frontside during fabrication. The otherdielectric layer is a backside dielectric layer 30 which correspondswith (or in other words is located at) a wafer backside duringfabrication. The semiconductor layer thus has a backside surface 36which faces (or is located at or on) the wafer backside and a frontsidesurface 38 which faces (or is located at or on) the wafer frontsideduring fabrication. The frontside dielectric layer is coupled with thefrontside surface of the semiconductor layer and the backside dielectriclayer is coupled with the backside surface of the semiconductor layer.

Although silicon-based semiconductor layers and dielectric layers areused in the representative examples, in other implementationsnon-silicon-based semiconductor layers and/or dielectric layers could beused as well. The elements of image sensors disclosed herein, however,may be useful to allow the formation of infrared (IR) sensors usingsilicon-based semiconductor layers, which layers in and of themselvesare generally incapable of IR sensing due to the bandgap properties ofsilicon. However, various image sensor implementations may be utilizedto detect visible and human invisible light (i.e., ultraviolet, etc.)and any combination of visible and human invisible light.

In FIG. 2 there are two pixels 10 shown, a first pixel 54 and a secondpixel 56. Such pixels may naturally be arranged in a line, in an array,or in any other arrangement in order to achieve an image sensor having aplurality of pixels arranged according to any desired configuration.

Each photodiode/pixel is associated with, or includes, a photodiodedepletion region 14. The photodiode depletion region 14 is generallylocated in a plane perpendicular with the page and is represented by thedashed line shown, having a maximum voltage (such as a pin voltage of asemiconductor device including the image sensor(s), or V_(PIN)) at thefrontside surface 38. A photodiode depletion potential 12, representedin the plane of the page by the other dashed line shown, with a barriershown at approximately the p-well region, is associated with each pixel.When an event occurs sufficient to create electron/hole pairs, anelectron flow 13 and a hole flow 15 are produced, and arerepresentatively depicted by the arrows shown, thus providing a currentto produce a signal associated with the pixel, as separated electronsare collected by the photodiode depletion field of the pixel.

A lens 22 and/or a light guide 26 may be included to refract, focusand/or otherwise convey light towards the pixel. Lens 22 inimplementations is a silicon nitride (SiN) microlens 24. In otherimplementations, the light guide 26/lens 22 may each be made of, bynon-limiting example, Si, TiO2, SiC or any other high index andnon-light absorbing material that has a low thermal conductivityrelative to materials such as metals. The light guide 26 is generallyhoused or situated within the backside dielectric layer 30. Anantireflective coating (ARC) 40 is included which reduces the percentageof light that is reflected back out of the light guide away from thepixel. An antireflective coating (ARC) 18 is also placed atop the lens22 to reduce the amount of light that is reflected back upwards at thelens surface. In implementations ARC 40 is formed of silicon dioxide(SiO₂). In other implementations ARC 40 could be formed of SiN, SiC,TiO₂, polycrystalline Si (poly-Si), amorphous Si (a-Si), or anothermaterial. In implementations the lens may be formed as a bump and theARC 18 may be formed as a coating on the bump. In implementations inwhich the lens is a bump it may be formed of the same material as thelight guide and both could be formed of one continuous element with nosurfaces therebetween.

The elements described thus far may be used to sense light within givenwavelengths. When the wavelength of light entering the lens/light guideis configured to create electron/hole pairs in the semiconductor layerdue to the characteristic band gap of the semiconductor material, acurrent will be produced and the light will be sensed, or, in otherwords, the light may be used to create a signal representative of thelight. Some wavelengths of light may be unable to produce a signal basedon the band gap of the semiconductor material. For example, some or allinfrared (IR) wavelengths generally will pass through a semiconductorlayer made of silicon without producing such a signal due to thespecific band gap of silicon.

In implementations of an image sensor 2/52, a light absorber layer 16 isplaced at the backside surface 36 and corresponds with the bottom of thelight guide. In the example shown in FIGS. 1-2 the light absorber layerhas the ARC 40 placed atop it. The light absorber layer is configured toabsorb light of a predetermined wavelength. In the representativeexamples shown in the drawings, the light absorber layer is specificallytailored to absorb light in the infrared (IR) region, though in otherimplementations it could be tailored to absorb light in any otherspectral regions of light, whether human visible or not. The lightabsorber layer is formed of a material that is configured to absorbphoton energy of incident light and convert the photon energy into heat.The generated heat then creates/facilitates creating electron/hole pairsto provide the current that is used to provide a signal and thereforesense the light. This process by which the light absorber layer absorbslight and generates heat to the pixel structure beneath it can bereferred to as photo-thermally coupling the light absorber layer withthe pixel.

In implementations the light absorber layer includes an electricallyconductive material (conductor). In implementations the light absorberlayer includes one or more of the following materials: Co; CoSi₂; Mo;MoSi₂; Ni; NiSi; Ni₂Si; NiSi₂, Pd; PdSi; Pd₂Si; Pt; PtSi; Ta; TaSi₂, Ti;TiSi₂, W; WSi; WSi₂; Zr; ZrSi₂; polycrystalline Si; Ge dopedmonocrystalline Si; Ge film on Ge doped silicon; GeSe film on Silicon;and/or any combination thereof. Many other materials may be used forsensing IR light so long as they have high absorption for lowerfrequencies of light. In implementations in which the light absorberlayer is a metal silicide and the semiconductor layer is a silicon-basedsemiconductor (such as monocrystalline or polycrystalline silicon), themetal silicide may act as a perfect or near perfectelectronic-vibrational heat transfer bridge between the metal and thesilicon, and may ensure a fast (or the fastest) local heat transfer rateinto the pixel. In various implementations, the light absorber layer maybe referred to as including one or more narrow band semiconductors orconductors which act as highly efficient absorbers of incident radiationand converters of the absorbed energy to heat localized beneath thelayer. The semiconductor layer may be referred to as a broad bandsemiconductor that contains a pixel depletion region. This pixeldepletion region is a region with a built-in depletion field configuredto separate electron-hole pairs formed inside or at the boundary of thedepletion region of a given pixel at the location of the interface ofthe light absorber layer and the semiconductor layer. The heat generatedby the light absorber layer, as discussed herein, generateselectron-hole pairs in the pixel depletion region.

A material's ability to function well as material for a light absorberlayer may be predictable using the imaginary part of the complex indexof refraction—a higher “k” value corresponds to higher absorptionvalues. For example, FIG. 5 shows a graph 64 which plots exponential kvalues for TaSi₂ and monocrystalline Si (c-Si) against spectralwavelength. A formula for determining absorption is:Absorption=1−exp(−4πkd/λ); where d=thickness, λ=wavelength and k=theimaginary part of the refractive index.

From FIG. 5 it can be seen that 100% absorption in very thin TaSi₂happens in a very wide spectral range, about 10 to 100 times wider thanin monocrystalline silicon. This predicts that an image sensor for widerange IR sensing may be formed with one or more wide range IR sensitivepixels using a thin TaSi₂ layer as the light absorber layer. This may beformed as a BSI sensor. FIG. 6 shows a graph 66 which plots exponentialk values for a few metals, metal silicides (namely, TaSi₂, CoSi₂, MoSi₂,NiSi, Ni₂Si, W, Mo, Co, and Ti), and monocrystalline Si (c-Si) againstlight wavelength. Each metal and silicide plotted exhibits anexponential absorption coefficient at least about 100-1,000 times higherthan that in monocrystalline Si and would allow the detection of photonsin a much wider spectral range—at least 100 times greater—thanmonocrystalline Si. The differences in absorption coefficient showssignificant predominance in conductor density of states (DOS) at the lowfrequency portion of the spectra responsible for fast, efficient heattransfer—thus equating to a very fast, localized heating effect in apixel. The k value is directly related to DOS and is often used inspectroscopy to estimate DOS.

Thus, the light absorber layer in implementations may include a highlyabsorptive, non-reflective (or low-reflective) thin layer conductor atthe back side integrated (BSI) side of a complementarymetal-oxide-semiconductor (CMOS) or CCD image sensor pixel to generate afast localized heating effect of the semiconductor material (such as Si)for greater electron/hole generation in the pixel/photodiode depletionregion. Spreading the light absorber layer laterally above, near orwithin the pixel photodiode depletion region (and/or centering the lightabsorber layer relative to the pixel) localizes heat for increasedelectron/hole pair generation at or near the interface of the lightabsorber layer with the semiconductor layer. Generated electron/holepairs are separated and signal electrons are collected using thephotodiode depletion field 12.

Energy from the absorbed photons is very quickly converted intonon-equilibrated pixel-localized heat. This absorption/conversion maylikely occur within a few picoseconds which is much faster than lateralheat dissipation in Si via phonons (approximately 10-15 THz). FIGS.18-20 show experimental observations in which even slower resistiveheating rates on the order of GHz generate laterally well-definedsignals (as “dark current” or “dark signal” images) from printed circuitboards of traditional image sensor pixel arrays. Thus “dark current” or“dark signal” which is exhibited in traditional image sensors isunintentionally captured, but with the image sensors 2, 52 disclosedherein, such dark current will be captured intentionally by absorptionof lower than Si bandgap photons in a light absorber layer. Accordingly,the image sensors utilizing light absorber layers allow the imaging oflong wavelengths of light even when these are outside of the Si bandgap.Upon absorption of IR photons with frequencies of about 30-500 THz(wavelengths of 10-0.6 micrometers) the increased local heating in thepixel will resulting in increased electron-hole pair generation comparedwith the aforementioned process related to traditional image sensors.

FIG. 18 shows a printed circuit board (PCB) 112 of a traditional imagesensor, the PCB having metal routing 114 giving off a “dark signal” fromresistive heating that is captured by the image sensor. FIGS. 19-10 showa printed circuit board (PCB) 116 of another traditional image sensorwith contact balls 118 formed of tungsten, the contact balls giving offa “dark signal” as captured by the traditional image sensor. Asindicated on the images, FIG. 19 is a low light capture (i.e., lowirradiation of the image sensor) and FIG. 20 is a no light capture(i.e., no irradiation of the image sensor). In each of these cases thedark signal is generated due to resistive heating of the elements of theimage sensor (or the PCB of the image sensor or a PCB coupled with theimage sensor). Thus, resistive heating of the metal routing in FIG. 18and resistive heating of the contact balls in FIGS. 19-20 creates thedark signals shown in the images. FIG. 18 was captured with a front sideilluminated sensor. FIGS. 19-20 were obtained at 70 degrees Celsius andreveal a non-uniformity among the contact balls. Such dark signals havealso been captured in BSI image sensor arrays from resistively heatedTiN plugs.

In the above cases of FIGS. 18-20 the dark signal is produced by aresistively heated conductor at the conductor/semiconductor (i.e.,conductor/Si) interface. In these cases wavelengths longer than themaximum wavelength for monocrystalline silicon (which is approximately1.2 microns), are detected as dark signals. FIG. 18 is a traditionalfront side image sensor producing a dark signal either though resistiveheating of the PCB routings or through long wavelength absorption. Inimplementations the image sensors 2, 52 and others disclosed hereincould be configured to detect dark signals of a PCB or other elementcoupled with the image sensor that create a “constant” dark image(noise) during use and to automatically correct for them.

In the image sensors 2, 52 and others disclosed herein, the lightabsorber layer placed at the BSI side of the semiconductor layer (suchas Si) in a BSI CMOS image sensor pixel enhances and extends the sensingcapability of a light sensor beyond the Si band gap to long lightwavelengths in the spectral range of about 0.7 to 20 microns.

In the implementations shown in FIGS. 1-2 the image sensors 2/52 arecomplementary metal-oxide-semiconductor (CMOS) sensors 120, though othertypes of devices could be used to form the image sensors 2/52 such ascharge-coupled device (CCD) sensors. When a CMOS sensor 120 is used, thedevice is becomes an enhanced IR sensitive BSI CMOS image sensor whichuses a local photon heating effect.

FIG. 3 is an image produced using a nanophotonic modeling software soldunder the trade name FDTD SOLUTIONS by Lumerical Solutions, Inc. ofVancouver, Canada. Variables used in the model were optimized to achieveabove 60% theoretical quantum efficiency (QE) and include, among others,the following parameters (which may also be used in actualimplementations of image sensors): the image sensor is a BSI sensor; theincident light is a 1500 nanometer (nm) wavelength plane wave of light;lens 22 has a radius of curvature of 1860 nm and a height of 640 nm andis made of SiN; ARC 18 is an SiO₂ ARC 20 and is 200 nm thick; thesemiconductor layer 34 is 2 micron thick silicon; the pixelwidth/diameter is 3 microns; the light absorber layer is a 160 nm thickTaSi₂ layer; the light guide is formed of SiN having an entrancediameter DIN of 1500 nm, an exit diameter D_(OUT) of 260 nm and a lengthfrom DIN to D_(OUT) of 3280 nm; the area/volume above the backsidedielectric layer is air; the ARC 40 is a 110 nm by 1800 nm SiC layer(n=2.6; k=0); the backside dielectric layer is, or is about, 3-4 micronsthick and is formed of SiO₂; the frontside dielectric layer is, or isabout, 4 microns thick and is formed of SiO₂, and; the shallow and deeptrenches are formed of SiO₂.

Not all of the elements of FIG. 2 are specifically pointed out in FIG.3, but the reader can envision where the various elements would belocated if the two images were superimposed. The backside dielectriclayer 30, semiconductor layer 34 and frontside dielectric layer 32 areindicated, and the position of the image sensors 2 and 52 are generallypointed to and their locations are evident from the light profile andfrom the previous FIG. 2 which has the same configuration for thevarious elements. As can be seen from the image in FIG. 3 produced bythe modeling software, the incident light 58, which in this case isinfrared (IR) light 60, is irradiated towards two image sensors, animage sensor 2 and an image sensor 52, both of which are backside imagesensors 6, but image sensor 2 has the shallow trench configuration whileimage sensor 52 has the deep trench configuration as discussed herein.The model shows a high intensity of the incident 1500 nm wavelengthlight before it hits the SiC/TaSi₂ interface.

The optical simulation shows intensity distribution of the 1500 nmlight. With respect to the lefthand image sensor 2, none of the 1500 nmlight is passing through the TaSi₂ layer, and this results in a pixelquantum efficiency (QE) of 62%, assuming that 100% of absorbed photonenergy is converted into un-equilibrated heat within the TaSi₂ lightabsorber layer 16. The model also shows little or zero absorption of1500 nm light in the silicon semiconductor layer, as the light intensityappears unchanged in the regions where the infrared light passes intoand through the silicon layer. The right hand image sensor 52 appears toshow similar properties. The two image sensors 2 and 52 appear to behavegenerally identically notwithstanding the deep trench configuration ofimage sensor 52 and the shallow trench configuration of image sensor 2.The region through which the 1500 nm light is blocked may be marginallyor negligibly larger for the image sensor 52 but, in general, isolationchoice does not appear to impact optical characteristics at 1500 nm.

The models above indicate that image sensors including the elementsdescribed herein may achieve a very high sensitivity (above 50% quantumefficiency (QE)) of infrared photons in a very wide spectral rangeincluding 0.7 to 20 micron wavelengths (beyond the Si band gap).

FIG. 4 shows an image created with a modeling software sold under thetrade name COMSOL MULTIPHYSICS by COMSOL, Inc. of Burlington, Mass. andusing the same parameters as those described above with respect to theFDTD SOLUTIONS model. The image shows temperature distribution 20nanoseconds after absorption of an incident 1500 nm light wave by thelight absorber layer. A heat scale 62 is shown and ranges from 24degrees Celsius (dark end) to 40 degrees Celsius (light end), andcorresponding colors in FIG. 3 therefore illustrate the temperaturedistribution. As can be seen, lateral heat dissipation is relativelyslow. The heat is fairly localized at 20 ns for both the light sensor onthe left with shallow trench isolation (shown by heated region 48) andthe light sensor on the right with deep trench isolation (shown byheated region 50). The heat is generally confined to the pixel area inboth cases. The light sensor with deep trench isolation on the right,however, shows a substantially improved confinement of the heat towithin the pixel active area, thus increasing its temperature higher andimproving its quantum efficiency (QE). This model assumes that 100% ofthe absorbed 1500 nm photon energy is converted into non-equilibratedlocalized heat within the pixel. Pixel quantum efficiency (QE) at 1500nm according to the model is 62%.

FIGS. 11A-17B show modeled time lapse images showing absorption,reflection, refraction, and pass-through of a pulse of 1500 nm lightusing the same variables as discussed above. FIGS. 11A, 12A, 13A, 14A,15A, 16A, and 17A show versions where the left hand image sensor 4 doesnot include a light absorber layer and includes shallow trenchisolation, while the right hand image does include a light absorberlayer and includes deep trench isolation. In FIGS. 11B, 12B, 13B, 14B,15B, 16B and 17B, the variables are exactly similar except that thelefthand image sensor does include a light absorber layer.

In FIGS. 11A and 11B the incident light 58, which in this model isinfrared (IR) light 60 of 1500 nm, has begun to pass through thebackside dielectric layer on the sides of the light guides and to berefracted (focused) by the lenses and light guides. In FIGS. 12A and 12Bthe passing of the light through the backside dielectric layer isfurther seen as well as further refraction/focusing by the light guides.In FIGS. 13A and 13B the light on the sides of the light guides is seenpartially passing through the semiconductor layer and partially beingreflected, while the light within the light guides in every case is seenas being further refracted/focused and being fully absorbed by the lightabsorber layers—except with regards to image sensor 4 wherein the lightis seen passing straight through the light guide into the semiconductorlayer. This generally continues with the remaining FIGS. 14A-17B—thelight is shown to pass straight through image sensor 4 and into thesemiconductor layer, through the semiconductor layer to the frontsidedielectric layer, and so forth. There is some refraction seen at eachlayer.

Thus, the modeled images of FIGS. 11A-17B show generally what would beexpected in light of the continuous irradiation model of FIG. 3, namely,none of the incident 1500 nm light pulse passes through the lightabsorption layers, but the image sensor 4 without a light absorber layerallows the light to pass straight through it and out into thesemiconductor layer, and out of the semiconductor layer into thefrontside dielectric layer. Image sensor 4 accordingly does not “sense”the infrared light pulse, as is the case with traditional silicon-basedimage sensors in general.

FIG. 7 shows an image sensor (sensor) 68 which includes a pair ofphotodiodes 70, each including a pixel 72 having a depletion region 74.First pixel 76 has a first depletion region (PD region) 78 and secondpixel 80 has a second depletion region (PD region) 82. The lightabsorber layers are seen between the backside surface 36 and the ARC 40.A transfer gate 84 electrically couples the separated electrons withelectrical routing 86 which is at least partially within the showndielectric layer 28, which is a frontside dielectric layer. In thisversion there is no backside dielectric layer shown. The backsidedielectric layer may be excluded, though in implementations there may bea backside dielectric layer which partially encapsulates the sides ofthe ARC 40 except at least for their top sides, as can be imagined. Theelectrical routing 86 may electrically couple the photodiode to anotherelement of the image sensor such as an amplifier, a processor, a memoryelement, and so forth. The electrical routing may additionally oralternatively couple the photodiode with any element outside of (orexternal to) the image sensor, such as an amplifier, a processor, amemory element, and so forth.

Notably, the image sensor(s) of FIG. 7 do not include any lenses orlight guides, but the light absorber layer is located directly on thesemiconductor layer and the ARC 40 is located directly on top of thelight absorber layer. Thus, this version does not include any focusingor light guiding elements. This architecture could be used in BSI imageCCD and CMOS image sensors, and may not require focusing elementsespecially in longer than max c-Si detection wavelength (i.e., largerthan approximately 1.2 microns).

FIG. 8 shows an image sensor 88 that is identical to image sensor 68except that a focusing element 90 is included within the frontsidedielectric. Focusing element 90 is a reflector 92 and reflected lightwaves 94 of the incident light 58 are shown being directed towards thelight absorber layer(s) thereby. Thus this image sensor includes afrontside reflecting focusing element which focuses the incident lighttowards a light absorber layer at the BSI side. In implementations thefocusing element 90 is a metal reflector or a multilayer dielectricreflector.

FIG. 9 shows an image sensor 96 which is similar to image sensor 68except including a backside dielectric layer 30 and a focusing element98, which is a lens 100. The lens 100 may be a microlens 102 which maysimply be a bump 106 in the dielectric material and may have anantireflective coating 104 placed thereon. The bump may be formed of thesame material as the backside dielectric layer and may have a refractiveindex greater than 1. In implementations the antireflective coating maybe omitted. Refracted light 108 is shown being directed towards thelight absorber material where it is absorbed.

Image sensor 110 of FIG. 10 is identical to image sensor 96 except thatit is a frontside device, with the light absorber material located atthe frontside surface 38 of the semiconductor layer, and with thetransfer gate 84 and electrical routing 86 located within the frontsidedielectric layer 32. This image sensor may particularly be an optionwhere larger pixels are used. In such implementations, the architecturemay be designed so as to avoid illuminating metal routings with theincident light.

Some implementations of image sensors implemented using componentsdisclosed herein may allow spectral collection in an extremely widerange (up to very long wavelengths in the far infrared (IR) rangegreater than 20 microns). For optimal conditions for any particularspectral range the choice of material for the light absorber layer andits thickness, as well as materials and sizes for the antireflectivecoatings, lenses, light guides, semiconductor layers, dielectric layers,and so forth, may be varied and or developed, and related changes inprocess flows may be undertaken as well.

In some implementations of image sensors some photons may be releasedfrom the light absorber layer from the light absorber layer itself beingheated, but the amount of photons may be small or negligible relative tothe incident light.

In places where the description above refers to particularimplementations of image sensors and related methods and implementingcomponents, sub-components, methods and sub-methods, it should bereadily apparent that a number of modifications may be made withoutdeparting from the spirit thereof and that these implementations,implementing components, sub-components, methods and sub-methods may beapplied to other image sensors and related methods.

What is claimed is:
 1. An image sensor, comprising: a semiconductorlayer, and; substantially all of a first side of a light absorber layerin direct contact with the semiconductor layer at a pixel of the imagesensor, the light absorber layer configured to absorb incident light andto substantially prevent the incident light from entering thesemiconductor layer; wherein the light absorber layer is substantiallyparallel with a plane formed by the semiconductor layer; and wherein thelight absorber layer is configured to heat a region of the semiconductorlayer in direct contact with the light absorber layer through absorbingthe incident light and to create electron/hole pairs in the regionthereby.
 2. The image sensor of claim 1, further comprising: amicrolens, the light absorber layer coupled between the microlens andthe semiconductor layer, the microlens configured to refract theincident light towards the light absorber layer; and a guide coupledbetween the microlens and the light absorber layer and configured toconvey the refracted light to the light absorber layer.
 3. The imagesensor of claim 1, wherein the image sensor comprises a backsideintegrated (BSI) sensor.
 4. The image sensor of claim 1, wherein thelight absorber layer is positioned between two shallow trenches in thesemiconductor layer, each shallow trench extending only partiallythrough the semiconductor layer from a backside of the semiconductorlayer towards a frontside of the semiconductor layer.
 5. The imagesensor of claim 1, wherein the light absorber layer is positionedbetween two deep trenches of the semiconductor layer, each deep trenchextending fully through the semiconductor layer from a backside of thesemiconductor layer through to a frontside of the semiconductor layer.6. An image sensor, comprising: a photodiode comprised at leastpartially within a semiconductor layer, and; substantially all of afirst side of a light absorber layer in direct contact with thesemiconductor layer, the light absorber layer configured to absorbincident light within predetermined wavelengths to substantially preventthe incident light from passing from the light absorber layer to thephotodiode; wherein the light absorber layer is substantially parallelwith a plane formed by the semiconductor layer; wherein the lightabsorber layer is configured to heat a depletion region of thephotodiode in response to absorbing the incident light and to createelectron/hole pairs in the depletion region thereby, and; wherein theimage sensor further comprises at least one dielectric layer coupledwith the semiconductor layer, and electrical routing coupled at leastpartially within the at least one dielectric layer which electricallycouples the photodiode with at least one other element of the imagesensor.
 7. The image sensor of claim 6, wherein the light absorber layeris comprised at a backside of the semiconductor layer, wherein the atleast one dielectric layer comprises a frontside dielectric layer and abackside dielectric layer, wherein the backside dielectric layer islocated at the backside of the semiconductor layer; wherein a focusingelement is comprised proximate the backside dielectric layer and isconfigured to focus the incident light through the backside dielectriclayer towards the light absorber layer; wherein the frontside dielectriclayer is comprised at a frontside of the semiconductor layer oppositethe backside of the semiconductor layer; and wherein the electricalrouting of the image sensor is comprised at least partially within thefrontside dielectric layer.
 8. The image sensor of claim 6, wherein thelight absorber layer is comprised at a frontside of the semiconductorlayer; the at least one dielectric layer comprises a frontsidedielectric layer coupled at the frontside of the semiconductor layer; afocusing element is comprised proximate the frontside dielectric layerand is configured to focus the incident light through the frontsidedielectric layer towards the light absorber layer; and the electricalrouting of the image sensor is comprised at least partially within thefrontside dielectric layer.